Excess dietary caloric intake from either fat or carbohydrate results in increased cell entry or synthesis of fatty acids (FA) and their activated products, acyl-CoAs. The incorporation of acyl-CoAs into triacylglycerol stores and lipoprotein secretion and their diminished entry into oxidation pathways contribute to nutrition- related disorders such as obesity, fatty liver, and atherosclerosis. Further, because both FA and acyl-CoAs are purported ligands for several nuclear transcription factors, dietary excess may alter fatty acid- and acyl- CoA-mediated regulation of a wide variety of cellular processes, including cell proliferation and neuronal function. In order to understand the effects of FA imbalance oh metabolism, we have been studying the long-chain acyl-CoA synthetases (ACSL) which promote FA uptake into cells and initiate virtually every pathway of FA metabolism. Our hypothesis that each isoform plays an independent role in channeling FA to specific pathways is supported by over-expression and knockdown studies. We now propose to investigate how the lack of one of the major acyl-CoA synthetase isoforms affects tissue and whole body metabolism. Using targeted gene disruption we have produced mice with liver and total body knockouts of ACSL1. We will study these ACSL1 null mice to determine the metabolic effects of ACSL1 lack a) on lipid metabolism and energy balance, and b) on FA- and acyl-CoA-mediated gene expression. A third objective will be to study the effects of overexpression and knockdown of other ACSL isoforms on FA uptake and metabolism in hepatocytes and adipocytes. The proposed studies will provide new insights into acyl-CoA metabolism, the effects of different dietary FA including essential FA, and disorders resulting from excess calories. They will enable us to understand how diet composition influences specific pathways of FA metabolism in liver, adipose tissue and heart to control metabolic pathways. Not only are the ACSL isoforms potential targets for the control of obesity, but their involvement in colon cancer and in genetic mental retardation shows that the proposed studies have practical relevance in the treatment of human disease. This research is relevant to obesity, fatty liver, diabetes, lipotoxicity, nutrient regulation of gene expression, cancer, and mental retardation.